Traditional incandescent light sources are provided with a tungsten filament which is made to glow by the passage of electric current. The filament is generally suspended near the center of a glass bulb, thereby providing a light intensity which is almost constant in all radial directions. The radial distribution of the light in combination with the high brightness of the filament, have in the past made the incandescent light sources popular for general lighting purposes like for instance for use in chandeliers. The crystals in chandeliers exhibit sparkling light effects which is considered as highly decorative.
However, incandescent light sources suffer from disadvantages such as short life span and a high power consumption.
Replacing incandescent light sources with LED light sources may alleviate or eliminate the above mentioned problems and provide a significant increase in efficacy. However, most LEDs are only capable of emitting light into a hemisphere (solid angle, Ω=2π sr), whereas incandescent light sources employing a glowing filament generally emit light uniformly almost into a full sphere (solid angle, Ω=4π sr).
U.S. Pat. No. 7,352,510 discloses a device comprising a first and a second light mixing component which are optically coupled via an optical focusing element for producing a light beam of uniform intensity and irradiance from a single or multi color source, e.g. a LED-array. The first light mixing element produces a uniform irradiance distribution of the light from the multi color source, while leaving the intensity distribution non-homogenous. The focusing element and the second light mixing component are used to homogenize the intensity distribution of the light beam received from the first light mixing element while the light intensity distribution with respect to the optical axis is substantially unaltered.